Three different topics have been studied under this project: (a) on the difficult problem of the effect of nearest-neighbor interactions on the steady-state kinetics of enzyme molecules in large lattices, an exact result derived in the last year is the calculation of the Onsager linear coefficient L in the flux-force relation for steady states near equilibrium of a one-dimensional lattice of two-state enzyme molecules; (b) a very complete theoretical analysis has been carried out of the ways in which microtubules and actin filaments can do mechanical work by lengthening, shortening, or treadmilling at constant length with a load attached; and (c) we have developed a cooperative model of the sarcoplasmic reticulum Ca-ATPase that fits equilibrium data on the binding of CA++ and H+ very well and we are in the process of attempting to fit steady-state ATPase data by the same model.